1. Field of the Invention
The present invention relates to an asynchronous transfer mode (ATM) communication system, and more particularly, to an ATM connectionless communication system having a session supervising function and a connection supervising function.
2. Description of the Related Art
Recently, Internet protocol traffic is accommodated in an ATM network, and the traffic is processed at a high speed by layer 2 switching. In a standard ATM communication system, which is connection-oriented, however, an inter-user connection needs to be explicitly set before data is transmitted from a source user terminal to a destination user terminal. Therefore, a connection establishing process is independent of a data transmitting process. In the connection establishing process, a switched virtual connection (SVC) is carried out. That is, a connection supervising process is carried out by using a global connection identifier (GCID) and an ATM layer cell label including a virtual path identifier (VPI) and a virtual channel identifier (VCI), so that one VCI is allocated to each link between the user terminals.
A prior art ATM connectionless communication system is based on ITU-T Recommendation I. 364 (see JP-A-74767). That is, a server unit and user units are connected by a transmission line. Data cells on links are multiplexed to two-layer logical connections. This will be explained later in more detail.
In the prior art ATM connectionless communication network system, a packet managements depends upon a connection management, and both the managements are carried out by the AAL. Therefore, it is impossible to identify cells and reconstruct packets therefrom, and thus, it is difficult to realize a multicast service.
Also, in the prior art ATM connectionless communication network system, a multipoint-to-multipoint connection realizing procedure is not defined as an ATM standard. As a result, the complexity of the multipoint-to-multipoint connection realizing procedure as well as the allocation of ATM connection (VCI) and the load of informing VCI to the user equipments may delay data transfer.
Further, in the prior art ATM connectionless communication network system, however, since a processing load is concentrated on the server unit, the processing ability of the server unit is a bottleneck in the processing of the entire system. Additionally, if the server unit becomes in a fault state, the entire system may be in a fault state.